NAME

       sched_setscheduler - set scheduling policy and parameters (REALTIME)

SYNOPSIS

       #include <sched.h>

       int sched_setscheduler(pid_t pid, int policy,
              const struct sched_param *param);

DESCRIPTION

       The  sched_setscheduler()  function  shall  set  the  scheduling  policy and scheduling parameters of the
       process specified by pid to policy and the parameters specified in the sched_param structure  pointed  to
       by  param, respectively. The value of the sched_priority member in the sched_param structure shall be any
       integer within the inclusive priority range for the scheduling policy specified by policy.  If the  value
       of pid is negative, the behavior of the sched_setscheduler() function is unspecified.

       The possible values for the policy parameter are defined in the <sched.h> header.

       If  a  process  specified by pid exists, and if the calling process has permission, the scheduling policy
       and scheduling parameters shall be set for the process whose process ID is equal to pid.

       If pid is zero, the scheduling policy and scheduling parameters shall be set for the calling process.

       The conditions under which one process has the appropriate privilege to change the scheduling  parameters
       of another process are implementation-defined.

       Implementations  may  require  that  the  requesting  process  have  permission to set its own scheduling
       parameters or those of another process. Additionally, implementation-defined restrictions may apply as to
       the appropriate privileges required to  set  a  process'  own  scheduling  policy,  or  another  process'
       scheduling policy, to a particular value.

       The sched_setscheduler() function shall be considered successful if it succeeds in setting the scheduling
       policy  and  scheduling  parameters of the process specified by pid to the values specified by policy and
       the structure pointed to by param, respectively.

       If  the  scheduling  policy  specified  by  policy  is  SCHED_SPORADIC,  the  value  specified   by   the
       sched_ss_low_priority  member  of  the  param argument shall be any integer within the inclusive priority
       range for the sporadic server policy. The sched_ss_repl_period and sched_ss_init_budget  members  of  the
       param  argument shall represent the time parameters used by the sporadic server scheduling policy for the
       target process. The sched_ss_max_repl member of the param argument shall represent the maximum number  of
       replenishments  that  are  allowed  to  be  pending  simultaneously  for the process scheduled under this
       scheduling policy.

       The specified sched_ss_repl_period shall be greater than or equal to the  specified  sched_ss_init_budget
       for the function to succeed; if it is not, then the function shall fail.

       The value of sched_ss_max_repl shall be within the inclusive range [1, {SS_REPL_MAX}] for the function to
       succeed; if not, the function shall fail.

       If the scheduling policy specified by policy is either SCHED_FIFO or SCHED_RR, the sched_ss_low_priority,
       sched_ss_repl_period,  and sched_ss_init_budget members of the param argument shall have no effect on the
       scheduling behavior.

       The effect of this function on individual threads is dependent on the scheduling contention scope of  the
       threads:

        * For  threads  with  system  scheduling contention scope, these functions shall have no effect on their
          scheduling.

        * For threads with process scheduling contention scope, the threads' scheduling  policy  and  associated
          parameters  shall not be affected. However, the scheduling of these threads with respect to threads in
          other processes may be dependent on the scheduling parameters of their  process,  which  are  governed
          using these functions.

       If  an  implementation  supports a two-level scheduling model in which library threads are multiplexed on
       top of several kernel-scheduled entities, then the underlying kernel-scheduled entities  for  the  system
       contention scope threads shall not be affected by these functions.

       The  underlying  kernel-scheduled  entities  for  the  process  contention scope threads shall have their
       scheduling policy and associated scheduling parameters changed to the  values  specified  in  policy  and
       param,  respectively.  Kernel-scheduled  entities  for  use  by process contention scope threads that are
       created after this call completes  shall  inherit  their  scheduling  policy  and  associated  scheduling
       parameters from the process.

       This  function  is  not  atomic  with  respect  to other threads in the process.  Threads may continue to
       execute while this function call is in the process of  changing  the  scheduling  policy  and  associated
       scheduling  parameters  for the underlying kernel-scheduled entities used by the process contention scope
       threads.

RETURN VALUE

       Upon successful completion, the function shall return the  former  scheduling  policy  of  the  specified
       process.  If  the sched_setscheduler() function fails to complete successfully, the policy and scheduling
       parameters shall remain unchanged, and the function shall return a value of -1 and set errno to  indicate
       the error.

ERRORS

       The sched_setscheduler() function shall fail if:

       EINVAL The  value of the policy parameter is invalid, or one or more of the parameters contained in param
              is outside the valid range for the specified scheduling policy.

       EPERM  The requesting process does not have permission to set either or both of the scheduling parameters
              or the scheduling policy of the specified process.

       ESRCH  No process can be found corresponding to that specified by pid.

       The following sections are informative.

EXAMPLES

       None.

APPLICATION USAGE

       None.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       sched_getparam()  ,  sched_getscheduler()  ,  sched_setparam()  ,  the   Base   Definitions   volume   of
       IEEE Std 1003.1-2001, <sched.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition,
       Standard  for  Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers,
       Inc and The Open Group. In the event of any discrepancy between this version and the  original  IEEE  and
       The  Open  Group  Standard,  the  original  IEEE and The Open Group Standard is the referee document. The
       original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group                                   2003                                 SCHED_SETSCHEDULER(P)